Methods for the preparation of heterogeneous supported metal catalysts by application of metal salt(s) solutions to a porous solids support component are well known. A typical first step in the preparation of a supported catalyst is to apply an aqueous solution of a salt of a catalytic metal, or metals, to the solids support. "Incipient wetness", sometimes referred to as "pore volume saturation", is a typical method of impregnating a solids support with the catalytic metal salt because it assures a higher dispersion of the metal salts within the pores of the support.
The incipient wetness technique requires the following steps, to wit: (1) forming a saturated aqueous solution of a salt of the catalytic metal, or metals, (2) contacting the support with a limited volume amount of the catalytic metal salt solution to imbibe the solution; the volume of the catalytic metal salt solution approaching but not exceeding the measured pore volume of the support, (3) removing the imbibed water from the support by thermal drying, (4) measuring the intermediate, lower pore volume of the support solids, and (5) repeating steps (1) through (4) until the desired metals loading is achieved, adjusting solution volumes between each cycle of steps to the lower pore volume.
While the conventional incipient wetness method is widely used, and has proven successful, the method is particularly laborious if salt solubility or support pore volumes are low, or high metals loadings are desired. Also, repeated cycles of drying lowers the available pore volume of the support, as a consequence of which the diffusional limitations of a catalyst are increased. Thus, an improved method of impregnating the porous solids support to obviate these prior art deficiencies in forming catalysts would prove beneficial, and supply a need of the industry.